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BLT8
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1989-08-31
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Using Clipper Applications on LANtastic
1. LANtastic and Clipper use the DOS 3.1 (and later) file and record
locking provided through the SHARE command. Something to note is
that a Clipper application must be written and compiled with this
in mind. Applications compiled with Clipper for use on LANs which
use their own proprietary file and record locking schemes (i.e.
Novell) will most likely not work without modification.
2. To open files in a sharable mode, issue the dBASE command SET
EXCLUSIVE OFF before issuing any dBASE USE commands.
3. The compiled executable files (xxx.exe) produced by the Clipper
compiler must be set to READ ONLY with the DOS ATTRIB command.
4. Clipper provides the following commands for locking records and
files:
RLOCK() Attempts to lock the current record of a file and
returns True if successful, False if not.
FLOCK() Attempts to lock the currently opened file and returns
True if successful, False if not.
NETERR() Returns a True value if two users attempt to add a
blank record to the end of a file at the same time, a
common occurrence in dBASE/Clipper applications.
5. A general issue with any multiuser database is: What happens when
a file or record is locked and that user's computer locks up or
for some reason is disconnected from the LAN? In Clipper
applications, SHARE takes care of the problem by noticing that the
user who locked the file or record has stopped accessing it, and
the lock is removed after about 15-30 seconds.
6. In the event of a LAN lockup or server crash, you will find it
necessary to rebuild the index files. Often, a entry being worked
on at the time of the crash will be completely lost. Both of
these problems are not related to LANtastic, but dBASE, and both
problems also occur in single user Clipper/dBASE applications.